Thermostat metal



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uHH-H ZO-OUQ INVENTOR. CLARENCE E ALBAN ATTORNEYS United States Patent nments, to W. M. Chace Company, a corporation of Delaware Filed Mar. 14, 1960, Set. No. 14,706 33 Claims. e1. 29-1955 I This invention relates to thermostat metals, and in particular to those composed of multiple metallic laminations, 111 WhlCh the component materials and their relative thicknesses are to be selected for simultaneously optimizing or controlling both the electrical resistivity and the temperature response of flexivity of the thermostat metal.

Numerous applications of thermostat metals require that electrical currents to be monitored, controlled, or limited, flow through the thermostat metal itself. In such instances t may, for example, be specified that the thermostat metal is to respond only to ambient temperature changes and not to the heat generated by the PR losses as the current flows through the element. To accomplish this, the resistivity of the thermostat metal must be quite low. Another related, and much broader, class of applications arises when the thermostat metal is to be employed as the actuating element in an electrical circuit breaker or interrupter. For these applications the thermostat metal must have a controlled and frequently low electrical resistivity, the latter attribute being necessary for controls with high current ratings. Furthermore, it is desirable to provide a number of related thermostat metals of graduated electrical resistivities so that circuit breaker and instrument designers can select a thermostat metal of the proper resistivity to match a particular current rating. Circuit breakers, for example, are usually manufactured in standard sizes for a wide range of current ratings, and it is therefore necessary to have available a series or family of related thermostat metals having similar mechanical properties and temperature response characteristics, but graduate delectrical resistivities so that actuating elements of the same physical size, but fabricated from different members of the thermostat metal family, can be employed to produce any current rating within a specified range.

The electrical resistivity of any conventional two-component thermostat metal, or bimetal, is relatively inflexible and not readily subject to control or reduction, since the component metals must be selected primarily for their diflerence in thermal coeflicient of expansion in order to achieve a composite material of adequate temperature response. To remedy this situation, a third layer, consisting of a low-resistivity metal, can be interposed between the two original laminations of the thermostat metal, resulting in a new composite material with reduced electrical resistivity. The fractional thickness of the center, low resistivity, lamination can be adjusted during manufacture to produce a family of related thermostat metals having a Wide range of electrical resistivities and still retain the optimum mechanical and thermal properties if the relative thicknesses of the two remaining laminations are properly selected.

Among the several objects of this invention are the establishment of a system or family of related thermostat metals having predetermined and graduated ressitivities, and at the same time the absolute maximum deflections in response to temperature change, while providing thermostat metals which are subject to relatively simple, practicable, and economical manufacture, yet demonstrate superior mechanical and thermal characteristics.

For each combination of materials employed in the three basic laminations making up the composite thermostat metal, and for each particular fractional thickness of the center, low-resistivity, lamination there is a unique relationship among the relative or fractional thicknesses Patented Sept. 3, 1963 of all laminations which must be satisfied to produce a composite material having the absolute maximum thermal response or flexivity. This invention will disclose and specify certain combinations of materials, and the pro portions in which these materials should be combined, as well as the manner of determining such proportions, in order to control the electrical resistivity of the composite thermostat metal While assuredly maintaining the maximum fiexivity.

In the drawings;

FIG. 1 is a side elevation of a thermostatic trimetal embodying the invention.

FIG. 1-A is an end elevation of the thermostatic trimetal shown in FIG. 1.

FIG. 2 is a side elevation of the thermostatic trimetal in elastically deformed condition after it has been subjected to a temperature change.

FIG. 3 is a side elevation of a thermostatic metal in the elastically deformed condition.

FIGS. 4 and 4-A are curves of flexivity versus percentage thickness of the outer :laminations.

FIGS. 5 and 5-A are curves of flexivity versus percentage thickness of the center component.

FIGS. 6 and 6-A are curves of percentage thickness of the outer laminations versus percentage thickness of the center components.

FIG. 7 is a metallurgical structural diagram of certain nickel-chromium-iron alloys.

Consider a thermostat metal composed of three basic laminations 1, 2, 3, FIG. 1, the center lamination of which consists of an alloy having a low electrical resistivity such, for example, as an alloy of 95% or more copper, or preferably 99% copper, 1% cadmium, or by way of further example, the center lamination can be nominally pure nickel. FIG. 1 is a side elevation and FIG. 1-A an end elevation of such thermostatic trimetal. Let one of the outside laminations consist of an alloy having a relatively low thermal coeflicient of expansion such as 'Invar, as in the preferred embodiment of this invention, and the other outside lamination consist of an alloy having a relatively high thermal coefiicient of expansion, for example, a nickel-chromium-iron alloy which might, as in the preferred embodiment of this invention, have the composition, 22% nickel-3% chromiu-m% iron. The electrical resistivity of the largely copper center lamination or the nickel center lamination is considerably lower than that of the other two laminations, and will thus be the controlling factor in determining the resistivity of the composite thermostat metal, according to the law of parallel resistances, viz.,

wh ere R==resistivity of the composite material A= fractional thickness of lamination #1 B=fractional thickness of lamination #2 C=fractional thickness of lamination #3 r =resistivity of lamination #1 r resistivity of lamination #2 r =resistivity of lamination #3 A+B+C=l 3, one another and to the center lamination, of the two outside laminations.

If a general analytical relationship existed between the flexivity and the dimensions and thermal and elastic properties of all three components in such a thermosta't metal, it would be possible to determine the optimum proportions in order to maximize the flexivity. Such a relationship has been developed, and its mathematical derivation is given here in an abbreviated form in order to illustrate'the fundamental physical laws involved and to provide the necessary background and understanding for proper application of the relationship.

Consider a length of thermostat metal, as shown in FIG. 1, composed of three basic layers of metal bonded to one another along their contiguous surfaces. When this assembly is subjected to a change in temperature, the internal moments created by the differences in thermal expansion, the elastic properties of the components, and the constraints occurring at the interfaces, will cause the element to bend. 'In general, the outermost laminat-ionsof the assembly are selected for the greatest practicable difierence in thermal ooefiicient of expansion,

while the center lamination is selected for its effect upon the electrical resistivity of the composite material.

. FIG. 2 illustrates the length of thermostat metal in the elastically deformed condition after it has been subjected to a temperature change AT. For the purpose of this analysis, the approximation will be made that the radiusof curvature is the same for each lamination of the three-component thermostat metal. This approximation is consistent with small deflection theory, and its validity is amply demonstrated by the fact that the fiexure equation developed here accurately predicts the experimentally measured performance of a wide variety of three-component thermostat metals. The same ap' proximation, incidentally, was employed by Timoshenko in his early analysis of the deflection characteristics of thermostatic bimetals. Thermos-tats, Journal of the Optical Society of America and Review of Scientific Instruments, vol. II, 1925, pp. 233-255.)

The thicknesses of the three Ibasic laminations will be expressed as dimensionless fractions of the total thickness, while the elastic moduli will be made dimensionless by expressing them as ratios of the modulus of the center lamination.

. where t=total thickness of the composite material and t t and i are the thicknesses respectively of laminations 1, 2 and 3, and E E and E are the moduli of elasticity respectively of laminations 1, 2, and 3 (Ref; 'Analysis of 'Bi-M'etal where b=width of thermostat metal.

It is evident that the adjacent fibers on the interface between laminations 1 and 2 must undergo the same net deformation. This deformation can be looked upon as being composed of three sub-deformations subject to the law of superposition. Each fiber expands or contracts due to (1) its thermal coefficient 'of expansion,

(2) the force F acting on its cross section, and (3) the strain as a result of bending. Thus,

where AT is the temperature change. Similarly, at the where t is the thickness of any lamination in the threecomponent thermostat metal.

Therefore,

Equating the right-hand members of Eqs. 12 and 13, and solving for P E bi A+2B+C B Solving Eq. 3 for P P E bt (DA +B +GC Solving Eq. 11 for P PgGC B Equating the right-hand members of Eqs. and 16 and solving for P t(DA +B +GC P2: 6;:(A+2B+C) A-l-B GO A+2B+C Ta- Equating the right-hand members of Eqs. 14 and 17 and solving for l/ p Employing the definition of flexivity, F, established by the American Society for Testing Materials, as the change in curvature per degree Fahrenheit for a thermostat metal of unit thickness Equation 20 expresses the flexivity of the threecomponent thermostat metal as a function of the thermal and elastic constants and the dimensionless thicknesses of the laminations. For a particular thickness of the center, resistivity-controlling lamination, it is desirable to proportion the thicknesses of the other two laminations so that the flexivity is a maximum. Since the form of Eq. 20 does not lend itself to analytical diiferentiation, point-by-point solutions can be made and the results plotted to permit locating the maxima graphically. The elastic and thermal constants for all three laminations are substituted into the equation, along with an arbitrarily selected thickness of the center lamination. Then particular values of the outer lamination thicknesses are successively substituted, and the equation solved numerically for flexivity. The results can be plotted as in FIGS. 4 and 4-A, from which the point corresponding to maximum flexivity is readily apparent. In FIG. 4 the center lamination is the herein specified copper alloy and in FIG. 4A the center lamination is nominally pure nickel, the other laminations in both FIGS. 4 and 4-A being Invar and a nickel-chromium-iron alloy as above specified. This process is repeated with new values of the center lamination thickness until the field of maxima has been completely explored.

Maximum flexivity as a function of the center or low resistance lamination thickness (obtained by taking one data point from each of a series of graphs such as exemplified by FIG. 4) is illustrated in FIG. 5 for a threecomponent thermostat metal with a center lamination composed of 99% copper-1% cadmium, with one outside lamination consisting of Invar, and with the other outside lamination consisting of a 22% nickel3% chromium75% iron alloy, as in the preferred embodiment of this invention; and FIG. 5-A illustrates maximum flexivity as a function of the center lamination thickness for a three-component thermostat metal With a substantially pure nickel-center lamination as described in this invention. In each of FIGS. 5 and 5-A the variation of the electrical resistivity of the thermostat metal is included on the same graph for convenience.

FIG. 6 (center lamination of copper) and FIG.' 6-A (center lamination of nickel) each illustrates the unique proportions for all three laminations which will result in a family of related thermostat metals characterized by each member of the family having the maximum flexivity possible for the component materials involved and for its particular resistivity as determined by the fractional thickness of the center lamination.

1n the past, as exemplified by United States Patent No. 2,240,824, it was the practice to proportion the relative thicknesses of three-component thermostat metals so that the sum of the thicknesses of the high-expanding components constituted essentially one-half of the total thickness of the composite material. The three-component vfiexivity equation given abovehas demonstrated that the thermal activity or flexivity of a three-component thermostat metal can be increased still further and, in fact, can be brought to its absolute maximum, by scientifically proportioning the individual laminatio-ns according to that relationship. The additional gain in thermal activity results from the fact that all times laminations have difiierent elastic moduli and different thermal coefficients of expansion, and therefore, the center lamination cannot precisely be categorized as either a part of the high-expanding or low-expanding side, even though it may in some instances have properties much more nearly equal to one of the outermost laminations than to the other.

The three-component flexivity equation is perfectly general, and accounts for the actual mechanical and thermal properties of each lamination, regardless of the magnitudes involved, and does not require any approximations or semi-arbitrary classifications of the components into high or low expanding categories. The subject equation will actually calculate the flexivity of any threecomponent material or two-component material, irrespective of the order or arrangement of the laminations and irrespective of their chemical compositions or mechanical or thermal properties.

If one desires to fabricate a thermostat metal having a desired electrical resistivity, by way of example, 150 ohms per circular mil foot, and a maximum flexivity where the outer lo-w expanding lamination is made of Invar, the outer high expanding lamination of a nickel-chromiumiron alloy as specified above, and a center lamination of substantially pure nickel, one need only refer to FIGS. S-A and 6A. FIG. 5A shows that such a thermostatic metal having a resistivity of 150 ohms per circular mil foot has a nickel center component or lamination with a thickness. that constitutes about 26.5% of the total thick ness of the thermostat metal and that the thermostatic metal has a flexivity of about 13.7 10 Now referring to FIG. 6-A it will be seen that Where the thickness of the center nickel component is 26.5% the graph for the high expanding side intersects the ordinate for such 26.5 at about the 31% abscissa and the graph of the low expanding side intersects the ordinate of said 26.5% at the 42.5% abscissa. Therefore after once determining that the thickness of the center component will be 26.5% of the total thickness of the laminated thermostat metal, by reading the graphs for the high expanding and low expanding sides in FIG. 6-A one can immediately determine that the thickness of the high expanding lamination will be 31% and that of the low expanding lamination 42.5% This same procedure can be followed with reference to FIGS. 5 and 6 for determining the relative thicknesses of p the high, low and center laminations of a laminated metal having a predetermined or desired resistivity 'Where the center lamination is at least copper as specified above and the outer laminations have thesame composition as referred to above with respect to FIGS. 5-A and 6A. The same procedure, with dilierent graphs, would be followed if the center lamination were, for example, pure iron or cobalt.

In order that the three-component thermostat metal which is the subject of this invention function properly in a circuit breaker or other electrical control device, it is not only necessary to proportion the relative thicknesses as described herein for predetermined electrical resistivity and. maximum fiexivity, but it is also imperative that the three laminations be positively bonded over the entire area of their contiguous surfaces so that the resultant composite material acts as an integral whole. The ability of a thermostat metal to exhibit maximum deflection with a change in temperature is completely dependent upon the forces and bending moments which are developed within the material, and these are in turn dependent upon the bonding of the larninations to one another. The dependency of the action of a thermostat metal upon the constraints applied through the bonds at the interfaces between the larninations is clearly demonstrated in the derivation of the three-component fiexivity equation.

Where the center lamination contains 95% or more copper, balance cadmium, one outer lamination of lnvar and the other outer lamination is a nickel-chromium-iron alloy, it has been determined from a great many experiments in bonding that the ultimate in bond strength is obtained for the specific three-component thermostat metal described in this invention by forming an ingot consisting of layers of the three basic components with a thin, 0.001- inch to ODDS-inch, layer of a diflusion-augmenting alloy applied in the interfaces between the two outside laminations and the center lamination. The difiusion-augmenting alloy is composed of from 70% to 95% copper with the balance substantially manganese, the preferred composition being 85% copper-l manganese. The composite ingot is subsequently heated in a controlled atmosphere under pressure to a temperature corresponding to the liquidus-solidus region of the phase diagram for the difiusionaugmenting alloy to produce diffusion welding in the solid state. Thus, the bond which forms between any two adjacent basic laminations is created by mutual cross diffusion and exchange of atoms between the laminations, augmented and accelerated by the presence of the thin layer of copper-manganese alloy, and as a result, the bond strength is equal to or greater than that of (the materials in the basic laminations themselves. It is imperative that the temperature during the diffusion Welding process be carefully controlled so as to be slightly above the solidus line and into the liquidns-solidus region for the diifusiomaugmenting alloy. The liquidus and solidus lines can be obtained experimentally or from published phase diagrams. Under the conditions described here, the difiusion-augmenting alloy, and for certain compositions, the low-resistivity center lamination alloy, will be in a state which can be likened to a sponge, with a solid matrix containing the liquid phase. The liquid phase has 'a very significant effect on this type of diffusion welding in the solid state because atomic diffusion coefiicients increase greatly when there is a liquid phase present.

The temperature during diffusion welding must not, however, at any time be great enough to produce melting of one of the basic laminations, since this would destroy the carefully prescribed relative thicknesses which are necessary for obtaining the contnolled electrical resistivity and simultaneous maximum flexivity, which are characteristics of the improved thermostat metals in this invention.

The diffusion-augmenting alloy is to be employed in very thin layers, representing [a negligible thickness in comparison with the basic l arninations in the three-component thermostat metal. Furthermore, upon completion of the diffusion welding process, the diffusion-augmenting alloy will not be detectably present, having been dispersed and completely absorbed in the adjacent l-aminations. Because of these considerations, it is unnecessary to account for the presence .of this alloy in determining the fractional thicknesses of the basic laminations for controlled resistivity and maximum fiexivity.

Where the center lamination is of nominally pure nickel and one outer lamination is lnvar and the other outer lamination a nickel-chromium-iron alloy, it has been determined [from a great many experiments in bonding that the ultimate in bond strength is obtained for the three-component thermostat metal described in this invention by forming an ingot consisting of layers of the three-components and subsequently subjecting the ingot to a combination of pressure and temperature under a controlled atmosphere to produce diffusion welding in the solid state. Thus the bond which forms between any two adjacent laminations is created by mutual cross diffusion and exchange of atoms between the laminations, and as a result, the bond strength is equal to or greater than that of the materials in the laminations themselves. It is imperative that the temperature during the diffusion Welding process remain below the melting temperature of the lowest melting point component in the thermostat metal, otherwise the carefully selected thickness proportions will be altered or destroyed due to the flow of one or more components, and the composite material will fail to exhibit the desired resistivity and flexivity characteristics.

The preferred embodiments of this invention includes a three-component thermostat metal with a center lamination consisting either of a 99% copper-4% cadmium alloy or of nominally pure nickel. The tfunction of this center lamination is to permit the manufacture of a family of thermostat metals which in general is characterized by comparatively low electrical resist-ivities, and more specifically, by graduated electrical resistivities among the various members of the family. This center lamination should have a lower electrical resistivity than the other two laminations and although preferably this low resistivity lamination is the center lamination it can, however, as stated above, be an outer lamination. Other low resistivity metals such as iron, cobalt, aluminum, chromium, silver, :gold, platinum, molybdenum, manganese, magnesium, titanium, tin, tungsten, or tantalum, can be substituted for the nickel in the center lamination without altering the general character or purpose of the invention. The remaining two laminations of the thermostat metal are selected primarily for their difference in thermal coefficient of expansion.

The material selected for the low-expanding side should have, in addition to the lowest practicable thermal coefficient of expansion, the following characteristics: suitability lfor diffusion welding with the copper-cadmium center lamination in the presence of the diffusion-augmenting alloy (no diffiusion-aulgmenting alloy is neces sary where the center lamination is nickel), metallurgical stability over a wide range of temperatures, good rolling and forming properties, high mechanical strength, adaptability to brazing or welding of electrical contacts, and reasonable corrosion resistance, to mention a few. In general it has been :found that the nickel-iron alloys having a nickel content ranging from 34% to 50% satisfy these requirements in varying degrees for the low expanding lamination. In the preferred embodiment of the invention, the material for the low-expanding side is Invar, with 36% nickel and the remainder substantially iron. However, the low expanding side in the thermostatic laminated metal comprising my invention can be any of the materials of known compositions having the above qualities and which have been used for the low expanding side'or lamination in thermostatic laminated metal.

Materials employed for the high-expanding side have similar requirements in terms of diffusion welding compatibility with the nickel center lamination or with the copper-cadmium center lamination in the presence of the diffusion-augmenting alloy, metallurgical stability, rolling and [forming properties, mechanical strength, corrosion resistance, and suitability for welding or brazing of electrical contacts, as well as the need for a high thermal coefiicient of expansion. Among such materials are the nickel-chromium-iron alloys having a nickel content ranging from to 35%, and a chromium content ranging from 1% to with the balance substantially iron. FIG. 7 is the metallungical structural diagram for these alloys. The region bounded by the heavy dashed line includes the more suitable alloys for the high-expanding side of the three-component thermostat metal which is the object of this invention. The composition of the high-expanding side for the preferred embodiment of this invention is 22% nickel3% chromium-75% iron, and is indicated by a small circle on the structural diagram.

Another suitable composition for the high expanding side or lamination is preferably 72% manganese-18% copper-10% nickel and the other alloys set (forth in the United States patent to Dean 2,349,577. However, the high-expanding side in the thermostaitc laminated metal comprising my invention can be any of the mate rials of known compositions having the above qualities and which have been used for the high expanding side or lamination in thermostatic laminated metal.

This invention describes a new and improved series or family of related thermostat metals, characterized generally by comparatively low electrical resistivities, and also by graduated electrical resistivities among the various members of lihfi family, with each member of the family exhibiting the absolute maximum thermal activity,

l or ilexivity, for the particular resistivity and component materials involved. This family of thermostat metals is generally composed of three basiclaminations, the relative or fractional thicknesses of the laminations being precisely controlled in order to achieve a predetermined electrical resistivity and maximum fiexivity.

The center lamination of one of the thermostat metals exemplifying this invention is composed of nickel or an alloy of preferably 98% or-more copper (however the copper content can be as low as 95%), with the balance cadmium, silver, or other metal of suitable low electrical resistivity, and its thickness as a fraction of the total thickness of the composite material is determined by the desired electrical resistivity for each member of the family according to the law of parallel resistances. This thickness of the center lamination may vary from zero to 60% of the total thickness to provide a corresponding range of resistivities in the members of the family. The remaining two laminations are nickel-iron and nickelchromiumdron alloys as specified herein, the composition being generally selected to produce a large difference in thermal coeflicient of expansion between the high-expandin-g side and the low-expanding side. The fractional thickness of each of the outside laminations is selected for each member of the family in accordance with the three-component flexivity equation, derived herein, to produce in each instance the maximum fiexivity. All three laminations are joined into an integral whole by diifusion welding in the solid state as above described.

The result is a family of superior thermostat metals, each having the uniquely optimum combination of electrical resistivity and fiexivity, while retaining all of the general properties desirable in any thermostat metal.

I claim:

1. A thermostatic laminated metal comprising a low expanding metal lamination, a high expanding metal lamination, and a metal lamination having a lower electrical resistivity than said low expanding and high expanding laminations, the relative thicknesses of said laminations being proportioned to produce the maximum available flexivity for the thermostatic laminated metal according to the following formula t is the overall thickness of the thermostatic laminated metal, t is the thickness of one lamination,

I is the thickness of a second lamination, and Z 10 is the thickness of a third lamination, E is the modulus of elasticity, E is the modulus of elasticity of one lamination, E is the modulus of elasticity of a second lamination, and E is the modulus of elasticity of a third lamination, a is the temperature coeflicient of expansion of one lamination, a is the temperature coeflicient of expansion of a second lamination, a is the temperature coefficient of expansion of a third lamination, Q=DA[B(A+B)+GC(B+1)], R=GC[B(1A) +DA(B+1)], Z=(DA +B +GC )(DA+B+GC), F is the fiexivity of the thermostatic laminated metal.

2. The thermostatic laminated metal claimed in claim 1 wherein the lowresistance lamination is made of a material having a low electrical resistivity on the order of the resistivity of a metal selected from the group consisting of nominally pure nickel and an alloy comprising 95% copper and the balance cadmium, the low expanding lamination is a nickel-iron alloy having a nickel content falling within a range of from 34% to 50% and the balance iron, and the high expanding lamination is a nickel-chromium-iron alloy having a nickel content falling within a range of from 15% to 35%, a chromium content falling within a range of from 1% to 20%, with the balance substantially iron.

3. The thermostatic laminated metal claimed in claim 2 wherein the low resistance lamination is a copper alloy having a copper content of at least 95% and the balance a metal having a low resistivity on the order of the resistivity of cadmium and silver.

4. The thermostatic laminated metal claimed in claim 1 wherein the lamination having a low electrical resistivity is the center lamination.

5. The thermostatic laminated metal as claimed in claim 2 wherein the thickness of the lamination having a low electrical resistance falls within .a range from 0 to of the total thickness of the thermostatic laminated metal.

6. The thermostatic laminated metal as claimed in claim 2 wherein the said laminations are difiusion welded in the solid state over the entire area of their contiguous surfaces whereby the resultant composite metal acts as an integral Whole.

7. A thermostatic laminated metal comprising a low expanding metal lamination, a high expanding metal lamination, and a metal lamination having a lower electrical resistivity than said low expanding and high expanding laminations, the fractional thickness of the lamination having low electrical resistivity falling within a range from 0 to 60% of the total thickness of the laminated metal and being proportioned according to the relationship 1 A B o irri an to produce a predetermined electrical resistivity for the thermostatic laminated metal, and the fractional thicknesses of the other tWo laminations being proportioned to produce the maximum available flexivity for the thermostatic laminated metal according to the following formula 2"- 1)Q+( a z) +3( )Q+ wherein A t /l, B t /Z, CZZI3/Z, D=E1/E2, G Eg/Ez, t is the overall thickness of the thermostatic laminated metal, f is the thickness of one lamination, t is the thickness of a second lamination, and t is the thickness of a third lamination, E is the modulus of elasticity, E is the modulus of elasticity of one lamination, E is the modulus of elasticity of a second lamination, and E is the modulus of elasticity of a third lamination, a is the temper-ature coeflicient of expansion of one lamination, 0: is'the temperature coefficient of expansion of a second lamination, 0: is the temperature coefiicient of expansion of a third lamination, Q=DA[B(A+B) +GC(B+1)],

11 R=GC[B(1A)+DA(B+1)], Z=(DA +B +GC (DA-l-B-l-GC), F is the flexivity of the thermostatic laminated metal.

8. The combinationcla-imed in claim 7 wherein the lamination having a low electrical resistivity is the center lamination.

9. The thermostatic laminated metal claimed in claim 7 wherein the low resistance lamination is made of a material having a low electrical resistivity on the order of the resistivity of a metal selected from the group con sisting of nominally pure nickel and an alloy comprising 95% copper and the balance cadmium, the low expanding lamination is a nickel-iron tall-y having a nickel content falling within a range of from 34% to 50% and the balance iron, and the high expanding lamination is a nickel-chromium-iron alloy having a nickel content falling within a range of from 15% to 35%, a chromium content falling within a range of from 1% to 20%, with.

the balance substantially iron.

10. The thermostatic laminated metal claimed in claim 9 wherein the low resistance lamination is a copper alloy having a copper content of at least 95% and the balance a metal having a low resistivity on the order of the resistivity of cadmium and silver.

I 11. The thermostatic laminated metal claimed in claim 8 wherein the low resistance lamination is a substantially pure metal selected from the group consisting of nickel, copper, iron, cobalt, aluminum, chromium, silver, gold, platinum, molybdenum, manganese, magnesium, titanium, tin, tungsten, and tantalum.

12. The method for making thermostatic laminated metal comprising a low expanding metal lamination, a high expanding metal lamination, and a metal lamination having a lower electrical resistivity than said low expanding and high expanding laminations comprising the steps of proportioning the relative thicknesses of said laminations to produce the maximum available flexivity for the thermostatic laminated metal according to the following formula I is the overall thickness of the thermostatic laminated metal, I; is the thickness of one lamination, 1 is the thickness of a second lamination, and I is the thickness of a third lamination, E is the modulus of elasticity, E

is the modulus of elasticity of one lamination, E is the tion, 04 is the temperature coefiicient of expansion of a second lamination, (x is the temperature coefficient of expansion of a third lamination,

F is the flexivity of the thermostatic laminated metal, then bringing the three laminations into surface to surface contact, and then diffusion welding in the solid state over the entire area of their contiguous surfaces the three laminations so that the resultant composite laminated metal acts as an integral whole.

13. The method claimed in claim 12 wherein the low resistance lamination is made of a material having a low electrical resistivity on the order of the resistivity of a metal selected from the group consisting of nominally pure nickel and an alloy comprising 95% copper and the balance cadmium, the low expanding lamination is a nickel-iron alloy having a nickel content falling within a range of from 34% to and the balance iron, and the high expanding lamination is a nickelchromium-iron alloy having a nickel content falling within a range of from 15% to 35 a chromium content falling within a range of from 1% to 20%, with the balance substantially iron.

14. The method claimed in claim 13 wherein the low resistance lamination is a copper alloy having a copper content of at least and the balance a metal having a low resistivity on the order of the resistivity of cadmium and silver.

15. The method claimed in claim 13 including the step of selecting, the lamination having a low electrical resistance so that it falls within a range of 0 to 60% of the total thickness of the thermostatic laminated metal. 7

16. The method set forth in claim 14 including the step of applying to each of the interfaces between the two laminations and the copper lamination a diti-usion augmenting alloy having a thickness falling within a range of the order of .001 inch to .005 inch and composed of 70% to 95% copper with the balance substantially manganese, heating the composite ingot in a controlled atmosphere under pressure to a temperature corresponding to the liquidus-solidus region of the phase diagram for the difliusion augmenting alloy to thereby produce diifusion welding of the three laminations in the solid state.

17. A thermostatic laminated metal comprising. an outer low expanding lamination of a nickel-iron alloy having a nickel content falling within a range of from 34% to 54% and the balance iron, an outer high expanding lamination of a nickel-chromium-iron alloy having a nickel content falling within a range of from 15% to 35% and a chromium content falling within a range of from 1% to 20%, with the balance substantially iron, and a center lamination of a copper alloy having a copper content of at least 95 and the balance a metal having a low resistivity on the order of the resistivity of cadmium andnsilver and thickness falling within a range of from 0 to 55% of the total thickness of the thermostatic metal, the relative thicknesses of the said outer lamin'ations being proportioned relative to any predetermined thickness of the center lamination to produce the maximum available flenivity for the thermostatic laminated metal as shown graphically in the drawing FIGURE 6.

18. A thermostatic laminated metal comprising an outer low expanding lamination of a nickel-iron alloy having a nickel content falling within a range of fro-m 34% to 54% and the balance iron, an outer high expanding lamination of a nickel-chromium-iron alloy having a nickel content falling within a range of from 15 to 35% and a chromium content falling within a range of from 1% to 20%, with the balance substantially iron, and a center lamination of a substantially pure metal selected from the group consisting of nickel, iron and cobalt and thickness falling Within a range of from *0 to 55% of the total thickness of the thermostatic metal, the relative thicknesses of the said outer laminations being proportioned relative to any predetermined thickness of the center lamination to produce the maximum available flexivity for the thermostatic laminated metal as shown graphically in the drawing FIGURE 6-A.

19. The thermostatic laminated metal claimed in claim 7 wherein the fractional thickness of the lamination having low electrical resistivity effectively approaches or equals Zero, the low resistance lamination is made of a material having a low electrical resistivity on the order of the resistivity of a metal selected from the group consisting of nominally pure nickel and an alloy comprising 95 copper and the balance cadmium, the low expanding lamination is a nickel-iron alloy having a nickel content falling within a range of from 34% to 54% and the balance iron, and the high expanding lamination is a nickel-chromium-iron alloy having a nickel content falling within a range of from 15% to 35%, a chromium content falling within a range of from 1% to 20% and the balance substantially iron.

20. The thermostatic laminated metal claimed in claim 19 wherein the low expanding lamination is a nickeliron alloy consisting substantially of 36% nickel and 64% iron; and the high expanding lamination is a nickel-chromium-iron alloy consisting substantially of 22% nickel, 3% chromium, and 75% iron.

21. The thermostatic laminated metal claimed in claim 7 wherein the fractional thickness of the lamination having low electrical resistivity elfectively approaches or equals Zero, the low resistance lamination is made of a material having a low electricalresistivity on the order of the resistivity of a metal selected from the group consisting of nominally pure nickel and an alloy comprising 95 copper and the balance cadmium, the low expanding lamination is a nickel-iron alloy having a nickel content falling within a range of from 34% to 54% and the balance iron, and the high expanding lamination is a manganese-copper-nickel alloy having a nickel content falling within arange of from 8% to 20%, a copper content falling within a range of from 7% to 19% and the balance manganese.

22. The thermostatic laminated metal claimed in claim 7 wherein the fractional thickness of the lamination having low electrical resistivity ellectively approaches or I equals Zero, the low resistance lamination is made .of a

material having a low electrical resistivity on the order of the resistivity of a metal selected from the group consisting of nominally pure nickel and an alloy comprising 95% copper and the balance cadmium, the low expanding lamination is a nickel-iron alloy having a nickel content falling within a range of from 34% to 54% and the balance iron, and the high expanding lamination is a manganese-oopper-nickel alloy consisting substantially of 72% manganese, 18% copper, and 10% nickel.

23. The thermostatic laminated metal claimed in claim 22 wherein the low expanding lamination is a nickeliron alloy consisting substantially of 36% nickel and 64% iron.

24. The thermostatic laminated metal claimed in claim 1 wherein the low resistance lamination is a substantially pure metal selected from the group consisting of nickel, copper, iron, cobalt, aluminum, chromium, silver, gold, platinum, molybdenum, manganese, magnesium, titanium, tin, tungsten and tantalum.

25. The thermostatic laminated metal claimed in claim 1 wherein the low resistance lamination is a copper alloy having a copper content of at least 95% and the balance a metal having a low resistivity on the order of the resistivity of cadmium and silver.

26. The thermostatic laminated metal claimed in claim 1 wherein the low resistance lamination is a copper alloy with a copper content of at least 95 and the balance a metal having a low electrical resistivity selected from the group consisting of cadmium and silver.

27. A thermostatic laminated metal comprising a low expanding lamination, a high expanding lamination, and a lamination having a low electrical resistivity, the relative thicknesses of said laminations being proportioned to produce the maximum available flexivity for the thermostatic laminated metal according to the following formula wherein A=t /z, B=t /t, C=t /t, D=E /E G=E /E t is the overall thickness of the thermostatic laminated metal, t is the thickness of one lamination, t is the thickness of a second lamination, and i is the thickness. of a third lamination, E is the modulus of elasticity, E is the modulus of elasticity of one lamination, E is the modulus of elasticity of a second lamination, and E is the modulus of elasticity of a third lamination, a is the temperature coefiicient of expansion of one lamination, a is the temperature coefiicient of expansion of a second 14 lamination, a is the temperature coefiicient of expansion of a third lamination, Q=DA[B(A+B)+GC(B+1)], R=GC[B(1-A)+DA(B+1)] z= (DA- +B +GC (DA +B+GC) F is the flexivity of the thermostatic laminated metal, the low expanding lamination being a nickel-iron alloy having a nickel content falling within a range of from 34% to 5 0% and the balance iron, the high expanding lamination being a nickel-chromium-iron alloy having a nickel content falling within a range of from 15% to 35%, a chromium content falling within a range of from 1% to 20%, with the balance substantially iron, said low resistance lamination being a substantially pure metal selected from the group consisting of nickel, copper, iron, cobalt, aluminum, chromium, silver, gold, platinum, molybdenum, manganese, magnesium, titanium, tin, tungsten, and tantalum.

28. A thermostatic laminated metal comprising a low expanding lamination, a high expanding lamination, and -a lamination having a low electrical resistivity, the relative thicknesses of said laminations being proportioned to produce the maximum available fiexivity for the thermostatic laminated metal according to the following formula lamination, a is the temperature coefiicient of expansion F is the flexivity of the thermostatic laminated metal, the low expanding lamination being a nickel-iron alloy having a nickel content falling within a range of from 34% to 50% and the balance iron, the high expanding lamination being a nickel-chromium-iron alloy having a nickel content falling Within a range of from 15% to 35%, a

. chromium content falling Within :a range of from 1% to 20%, with the balance substantially iron, the low resistance lamination being a copper alloy with a copper content of at least 95 and the balance a metal having a low electrical resistivity selected from the group consisting of cadmium and silver.

29. A thermostatic laminated metal comprising a low expanding lamination, a high expanding lamination, and a lamination having a low electrical resistivity, the relative thicknesses of said laminations being proportioned to produce the maximum available flexivity for the thermostatic laminated metal according to the following formula.

wherein A t /t, B=t2/t, C=t /Z D=E1/E2, G Eg/Eg, t is the over-all thickness of the thermostatic laminated metal, t is the thickness of one lamination, I is the thickness of a second lamination, and i is the thickness 15 of'a third lamination, Q=D'A[B(A+B)'+GC(B+1)L F is the flexivity of the thermostatic laminated metal, the low expanding lamination being a nickel-iron alloy having a nickel content falling within a range of from 34% to 50% andthe balance iron, the high expanding lamination being a nickel-chromium-iron alloy having a nickel content falling within a range of 'from 15% to 35%, a

chromium content falling within a range of from 1% to 20%, with the balance substantially iron, the thickness of the lamination having a low electrical resistance falling within a range from to 60% of the total thickness of the thermostatic laminated metal, the low resistance lamination consisting of substantially pure nickel.

30. A thermostatic laminated metal comprising a low expanding lamination, a high expanding lamination, and a lamination having a low electrical resistivity, the relative thicknesses of said laminations bein roportioned to produce the maximum available flexivity for the thermostatic laminated metal according to the following formula t is the overall thickness of the thermostatic laminated metal, t is the thickness of one lamination, 1 is the of a third lamination, E is the modulus of elasticity, E is the modulus of elasticity of one lamination, E is the modulus of elasticity of a second lamination, and E is the modulus of elasticity of a third lamination, a is the temperature coefficient of expansion of one lamination, 1x is the temperature coefficient of expansion of a second lamina-tion, a is the temperature coefficient of expansion of a third lamination, Q=DA[B(A+B)+GC(B+1)],

R=GC[B(1A)+DA(B+1)] Z: (DA +B -{GC (DA +B+GC) F is the flex-ivity of the thermostatic laminated metal, the low expanding lamination being a nickel-iron alloy having a nickel con-tent falling within a range of from 34% to 50% and the balance iron, the high expanding lamination being a nickel-chromium-iron alloy having a nickel content falling within a range of from 15 to 35%, a chromium content falling within a range of from 1% to 20%, with the balance substantially iron, the thickness of the lamination having a low electrical resistance falling within a range from 0 to 60% of the total thickness of the thermostatic laminated metal, the low resistance lamination being a copper-cadmium alloy consisting of substantially 99% copper and 1% cadmium.

31. A thermostatic laminated metal comprising a low expanding lamination, a high expanding lamination, and a lamination having a low electrical resistivity, the fractional thickness of the lamination having low electrical resistivity falling within a range from 0 to 60% of the total thickness of the laminated metal and being proportioned according to the relationship to produce a predetermined electrical resistivity for the thermostatic laminated metal, and the fractional thick-l nesses of the other two laminations being proportioned to produce the maximum available flexivity for the thermostatic laminated metal according to the following formula "thickness of a second lamination, and t is the thickness modulus of elasticity of one lamination, E is the modulus of elasticity of a second lamination, and E is the modulus of elasticity of a third lamination, a is the temperature coefficient of expansion of one lamination a is the temperature coefiicient of expansion of a second lamination, a is the temperature coefiicient of expansion of a third lamination,

F is the flexivity of the thermostatic laminated metal, the low expanding lamination being a nickel-iron alloy having a nickel content falling within a range of from 34% to 50% and the balance iron, the high expanding lamination being a nickel-'chromium-iron alloy having a nickel content falling within a range of from 15 to 35%, a chromium content falling within a range :of from 1% to 20 with the balance substantially iron, the low resistance lamination being a copper alloy with a copper content of at least 95% and the balance a metal having a low electrical resistivity selected from the group consisting of cadmium and silver.

32. The method for making themostatic laminated metal comprising a low expanding lamination, a high expanding lamination, and a lamination having a low electrical resistivity comprising the steps of proportioning the relative thicknesses of said laminations to produce the maxim-um available fiexivity for the thermostatic laminated metal accordingv to the following formula tion, a is the temperature coefiicient of expansion of a second lamination, a is the temperature coeflieient of expansion of a third lamination,

F is the flexivity of the thermostatic laminated metal, then bringing the three laminations into surface to surface contact, and then diffusion welding in the solid state over the entire area of their contiguous surfaces the three laminations so that the resultant composite laminated metal acts as an integral whole, the low expanding lamination being a nickel-iron alloy having a nickel content falling with a range of from 34% to 50% and the balance iron, the high expanding lamination beign a nickel chromium-iron alloy having a nickel content falling within a range of from 15% to 35%, a chromium content falling within a range of from 1% to'20%, with the'balance substantially iron, the low resistance lamination being a copper alloy with a copper content of at least and the "balance a metal having a low electrical resistivity selected from the group consisting of cadmium and silver.

33. The method for making thermostatic laminated metal comprising a low expanding lamination, a high expanding lamination, and a lamination having a low electrical resistivity comprising the steps of proportioning the relative thicknesses of said laminations to produce the maximum available flexivity for the thermostatic laminated metal according to the following fonrn ula 1 is the overall thickness of the thermostatic laminated metal, t is the thickness of one lamination, i is the thickness of a second lamination, and t is the thickness of a third lamination, E is the modulus of elasticity, E is the modulus of elasticity of one lamination, E is the modulus of elasticity of a second lamination, and E is the modulus of elasticity of a third lamination, a is the temperature coeffioient of expansion of one lamination, a is the temperature coeflioient of expansion of a second lamination, a is the temperature coeflicient of expansion of a third lamination,

Q=DA[B( R=GC[B(1A)+DA(B+1)] Z (DA- +B -l-GC (DA +B-I-GC) F is the fiexivity of the thermostatic laminated metal, then bringing the three laminations into surface to surface contact, and then diffusion welding in the solid state over the entire area of their contiguous surfaces the three laminations so that the resultant composite laminated metal acts as an integral whole, the low expanding lamination being a nickel-iron alloy having a nickel content falling with a range of from 34% to 50% and the balance iron, the high expanding lamination being a nickel-chromium-iron alloy having a nickel content falling within a range of from 15% to 35%, a chromium content falling within a range of from 1% to 20%, with the balance substantially iron, the low resistance lamination being a substantially pure metal selected from the group consisting of nickel, iron and cobalt.

References Cited in the file of this patent UNITED STATES PATENTS 1,996,721 Gibbs Apr. 2, 1935 2,240,824 Alban May 6, 1941 

1. A THEMOSTATIC LAMINATED METAL COMPRISING A LOW EXPANDING METAL LAMINATION, A HIGH EXPANDING METAL LAMINATION, AND A METAL LAMINATION HAVING A LOWER ELECTRICAL RESISTIVITY THAN SAID LOW EXPANDING AND HIGH EXPANDING LAINATIONS, THE RELATIVE THICKNESSES OF SAID LAMINATIONS BEING PROPORTIONED TO PRODUCE THE MAXIMUM AVAILABLE FLEXIVITY FOR THE THERMOSTATIC LAMINATED METAL ACCORDING TO THE FOLLOWING FORMULA 